The present invention relates to a display device which utilizes an emission of electrons into a vacuum, and more particularly, to a display device which can enhance the display characteristics by enabling the stable control of an electron emission quantity by forming a gap between electron emitting sources and control electrodes which controls the electron emission quantity from the electron emitting sources with high accuracy.
As a display device which exhibits the high brightness and the high definition, color cathode ray tubes have been widely used conventionally. However, along with the recent request for the higher quality of images of information processing equipment or television broadcasting, the demand for planar displays (panel displays) which are light in weight and require a small space while exhibiting the high brightness and the high definition has been increasing.
As typical examples, liquid crystal display devices, plasma display devices and the like have been put into practice. Further, particularly, as display devices which realize the higher brightness, it is expected that various kinds of panel-type display devices including a display device which utilizes an emission of electrons from electron emitting sources into a vacuum (hereinafter, referred to as xe2x80x9can electron emission type display devicexe2x80x9d or xe2x80x9ca field emission type display devicexe2x80x9d) and an organic EL display which is characterized by low power consumption will be commercialized.
Among such panel type display devices, as the above-mentioned field emission type display device, a display device having an electron emission structure which was invented by C. A. Spindt et al (for example, see U.S. Pat. No. 3,453,478, Japanese Patent Laid-open No. 2000-21305), a display device having an electron emission structure of a metal-insulator-metal (MIM) type, a display device having an electron emission structure which utilizes an electron emission phenomenon based on a quantum theory tunnelling effect (also referred to as xe2x80x9csurface conduction type electron emitting source, see Japanese Patent Laid-open No. 2000-21305), and a display device which utilizes an electron emission phenomenon having a diamond film, a graphite film and a carbon nanotube and the like have been known.
FIG. 29 is a cross-sectional view for explaining one constitutional example of a known field emission type display device, and FIG. 30A to FIG. 30B are explanatory views showing constitutional examples of an electron emission source of one pixel and a control electrode which controls an electron emission quantity from the electron emission source. The field emission type display device is constituted such that a sealing frame 300 is interposed and sealed between both inner peripheries of a rear panel 100 which forms field-emission type electron emitting sources 2a and control electrodes 4 over an inner surface thereof and a face panel 200 which form anodes 7 and a fluorescent material layer 6 on an inner surface thereof which faces the above-mentioned rear panel 100, and the inside which is defined by the rear panel 100, the face panel 200 and the sealing frame 300 is reduced to a pressure lower than an atmospheric pressure of an external field or is evacuated (hereinafter referred to as xe2x80x9cvacuumxe2x80x9d).
The rear panel 100 includes cathode wires 2 which have electron emitting sources 2a and the control electrodes 4 which are formed such that the control electrodes 4 cross the cathode wires 2 by way of an insulation layer 3 on the rear substrate 1 preferably made of glass or alumina or the like. Then, an electron emission quantity (including turning on or off of emission) from the electron emitting sources 2a are controlled in response to the potential difference between the cathode wires 2 and the control electrodes 4.
Further, the face panel 200 includes the anodes 7 and the fluorescent material layer 6 on a face substrate 5 formed of light-transmitting material such as glass. The sealing frame 300 is fixedly secured to the inner peripheries of the rear panel 100 and the face panel 200 using an adhesive such as frit glass. The inside defined by the rear panel 100, the face panel 200 and the sealing frame 300 is evacuated to a vacuum of 10xe2x88x925 to 10xe2x88x927 Torr, for example. A gap formed between the rear panel 100 and the face panel 200 is held by gap holding members 9.
The insulation layer 3 is interposed between the cathode wires 2 formed on the rear panel 100 and the control electrode 4 which cross the cathode wires 2 and an hole (grid hole) 4a is formed at each crossing portion of the cathode wire 2 and the control electrode 4. The hole 4a allows electrons emitted from the electron emitting source 2a to pass therethrough toward the anode side. On the other hand, the electron emitting source 2a is formed on the above-mentioned crossing portion of the cathode wire 2 and the control electrode 4 and an insulation layer 3 is eliminated at a portion which corresponds to the hole 4a of the control electrode 4. The above-mentioned electron emitting sources 2a are constituted of carbon nanotubes (CNT), diamond-like carbon (DLC) or other field emission cathode, for example.
Here, as the electron emitting sources 2a, light sources which use carbon nanotubes are illustrated. As shown in FIG. 30A and FIG. 30B, the electron emitting source 2a is formed right below the hole 4a of the control electrode 4. Although the case in which one electron emitting source 2a is formed per one pixel is illustrated in FIG. 30A and FIG. 30B, a plurality of electron emitting sources 2a may be formed per one pixel.
FIG. 31A and FIG. 31B are explanatory views corresponding to FIG. 30A to FIG. 30B which show a display device forming a plurality of electron emitting sources per one pixel. Here, a plurality of holes 4a are formed in the control electrode 4 and a plurality of electron emitting sources 2a are arranged on a cathode wire 2 corresponding to respective holes 4a. 
Electrons emitted from a rear panel 100 impinge on a fluorescent material layer 6 of an opposing face panel 200. Light which corresponds to the emitting characteristics of the fluorescent material layer 6 is irradiated to the outside of the face panel 200 and functions as a display device.
As literatures which disclose the conventional technique related to this type of display device, for example, Japanese Patent Laid-open No. 1999-144652, Japanese Patent Laid-open No. 2000-323078 and the like are named.
However, the display devices which have been explained in conjunction with FIG. 30A, FIG. 30B and FIG. 31A, FIG. 31B have following problems.
FIG. 32 is an enlarged cross-sectional view of one pixel portion for explaining a constitutional example of a rear panel of a conventional field emission type display device. In such a display device of this type, with respect to a rear panel 100, cathode wires 2 are formed on a rear substrate 1 by a thin film patterning technique, an insulation layer 3 having a given thickness is formed on the cathode wires 2, and the insulation layer 3 corresponding to pixel portions are removed. Then, control electrodes 4 are formed on the insulation layer 3 by a vapor deposition method or a sputtering method except for holes 4a. 
Since the insulation layer 3 is formed by coating resin material using a screen printing method, it is difficult to make a thickness of the insulation layer 3 uniform. Accordingly, it is impossible to obtain the uniform thickness with no irregularities over the entire surface of the display region. Since the control electrodes 4 are formed along the surface contour of the insulation layer 3, as emphasized in conjunction with FIG. 32, the irregularities are generated with respect to a gap defined between the cathode wires 2 and the control electrodes 4 due to the irregularities of the thickness of the insulation layer 3. It is necessary to control the gap between the cathode wires 2 and the control electrode 4 at a xcexcm level because the irregularities of the gap in the peripheries of the holes 4a of the control electrode 4 bring about the irregularities of electron emission abilities of individual pixels.
Further, since the insulation layer 3 is disposed between the crossing portions of the cathode wires 2 and the control electrodes 4, the capacitance is generated. The irregularities of the thickness of the insulation layer 3 lead to the irregularities of the capacitance and when the thickness of the insulation layer 3 is increased, this obstructs the high-frequency driving. Accordingly, the thinner the thickness of the insulation layer 3, the high-frequency driving is improved and hence, it is ultimately desirable to have the constitution which can eliminate the insulation layer 3. The conventional technique is less than optimal with respect to these matters in using the display device in an actual use and these matters constitute drawbacks to be solved.
Accordingly, it is an object of the present invention to provide a display device which can solve the above-mentioned problems of the conventional techniques and can realize the electron emission characteristics and the high-frequency driving of high performance by adopting a constitution in which a gap formed between cathode wires 2 (electron emitting sources 2a) and control electrodes 4 can be made uniform and a thickness of an insulation layer 3 disposed between them can be reduced or the insulation layer 3 can be eliminated.
To achieve the above-mentioned object, a display device according to the present invention constitutes control electrodes by forming recessed portions and holes in plate-like members and regulates a gap between cathode wires and control electrodes based on a plate-thickness-direction size of the holes.
Further, the reduction of capacitance is achieved by making portions of the control electrodes face the rear substrate directly or by interposing an insulation layer between the control electrodes and the cathode wires. Further, projecting portions or thin plate-thickness portions such as recessed portions are formed by etching or the like at hole portions of the control electrodes or portions of the control electrodes except for the hole portions or a distance between holes through which the flow of electrons passes and the cathode wires is controlled. To describe the fundamental constitutions of the present invention, they are as follows.
(1) In a display device comprising a rear panel having a plurality of cathode wires having electron emitting sources, a plurality of control electrodes which cross the cathode wires and control an emission quantity of electrons from the electron emitting sources in response to the potential difference between the cathode wires and the control electrodes and a rear substrate, and a face panel having anodes and fluorescent materials, the control electrodes are formed of plate-like members, the control electrodes have holes which allow the electrons emitted from the electron emitting sources to pass therethrough toward the face panel side in first regions which cross the cathode wires, and assuming a distance from the rear substrate to the holes of the control electrodes as xe2x80x9caxe2x80x9d and a distance from the rear substrate to the control electrodes as xe2x80x9cbxe2x80x9d, the control electrodes have second regions where a relationship a greater than b is established between the neighboring cathode wires.
The above-mentioned first regions correspond to pixel portions. Recessed portions including holes are formed by etching cathode-wire sides of the control electrodes and projecting portions (second regions) which project toward a rear substrate side remain between the neighboring recessed portions. A distance between the control electrodes and the cathode wires, that is, a gap is formed based on the distance xe2x80x9caxe2x80x9d from the rear substrate to the holes formed in the recessed portions. The gap is determined by a depth of etching and the gap which is the distance between the cathode wires and the control electrodes can be made uniform by forming recessed portions in the control electrodes by a uniform etching. Further, with the provision of the projecting portions, the insulation layer can be made thin or can be eliminated.
(2) In the constitution (1), the control electrodes are supported at the second regions.
(3) In the constitution (1) or (2), the control electrodes have recessed portions at the anode side in the first regions.
(4) In any one of the constitutions (1) to (3), an insulation layer is formed between the second regions and the rear substrate. By interposing the insulation layer between the portions of the control electrodes in which the recessed portions are not formed and the rear substrate, the gap adjustment and the electric insulation between the control electrodes and the cathode wires adjacent to the control electrodes can be ensured.
(5) In any one of the constitutions (1) to (4), the cathode wires are divided into two or more regions within one pixel and the control electrodes include the second region in each region defined between the divided cathode wires. In the constitution which divides one pixel, the portions projecting in the direction toward the rear substrate are formed between the divided portions in the same manner as portions formed between the neighboring pixels.
(6) In any one of the constitutions (1) to (5), the cathode wire includes an opening within one pixel and the control electrode has the second regions in the opening of the cathode wire. The projecting portions of the control electrodes are brought into contact with the rear substrate through the opening of the cathode wires.
(7) In any one of constitutions (1) to (6), the control electrodes are fixed to the rear panel by on adhesive. The control electrodes are formed by forming holes which allow electrons to pass therethrough and the recessed portions in metal material by etching and the control electrodes have both end peripheries thereof fixed to the rear substrate using an adhesive in the state that a tension is applied to the control electrodes in the longitudinal direction at the time of mounting the control electrodes to the rear substrate. Alternatively, the projecting portions of the control electrodes are fixed to the rear panel by an adhesive. Accordingly, the gap formed between the cathode wires and the control electrodes can be held uniform. The cathode wires can be fixed to the rear substrate by an anodic bonding.
(8) In any one of constitutions (1) to (7), the control electrode has the plurality of holes in one of the first regions. By arranging a plurality of electron emitting sources per one pixel, the uniform electron emission can be obtained.
(9) In the constitution (8), in one of the first regions, no insulation layer is provided between regions formed between the plurality of holes and the cathode wire. Since no insulation layer is provided between them, the capacitance between both electrodes can be reduced so that the display device is suitable for high-frequency driving.
(10) In a display device comprising a rear panel having a plurality of cathode wires having electron emitting sources, a plurality of control electrodes which cross the cathode wires and control an emission quantity of electrons from the electron emitting sources in response to the potential difference between the cathode wires and the control electrodes and a rear substrate, and a face panel having anodes and fluorescent materials, the control electrodes are formed of plate-like members, the control electrodes have third regions which are indented than other regions of the control electrodes in the thickness direction at positions where at least portions of the third regions are superposed on first regions where the control electrodes cross the cathode wires, and the control electrodes have holes which allow the electrons emitted from the electron emitting sources to pass therethrough in the first regions as well as in the third regions.
By forming the holes in the indentations, fine holes can be formed with high accuracy even when the thick plate-like member is used. Further, with the use of the plate-like member, the irregularities of the gap can be suppressed.
(11) In the constitution (10), assuming a distance from the rear substrate to the holes of the control electrodes as xe2x80x9caxe2x80x9d and a distance from the rear substrate to the control electrodes as xe2x80x9cbxe2x80x9d, the control electrodes have second regions where a relationship a greater than b is established between the neighboring cathode wires.
The control electrodes include the indentations at the cathode-wire side and have the projecting portions as the second regions and hence, the insulation layers can be made thin or can be eliminated.
(12) In the constitution (10) or (11), in the first regions, distances from the cathode wires to the first regions of the control electrodes are set substantially equal. This includes a case in which the indentations are formed at the anode side, a case in which the indentations are formed at the cathode wire side and over the whole first region, and a case in which both of these cases are combined.
(13) In the constitution (10) or (11), an insulation layer is formed between the cathode wires and the control electrodes in the first regions. By interposing the insulation layer between portions of the control electrodes where no indentations are formed and the cathode wires, the electric insulation between the cathode wires and the control electrodes is ensured.
(14) In the constitution (10) or (11), a thickness of widthwise end portions of the control electrodes is greater than a thickness of the holes in the first regions. The indentations are formed while except for the widthwise end portions.
(15) In the constitution (14), the insulation layer is disposed between the cathode wires and the control electrodes at the widthwise end portions in the first regions. The insulation between the cathode wires and the control electrodes can be ensured. Further, the control electrodes can be also supported by the insulation layers so that the control electrodes can be supported in a stable manner.
(16) In any one of the constitutions (10) to (15), the control electrodes include the plurality of holes in one of the first regions. By arranging a plurality of electron sources per one pixel, the uniform electron emission can be obtained.
(17) In any one the constitutions (10) to (16), the third regions are formed by etching. The control electrodes are formed by machining holes for allowing electrons to pass therethrough or indentations in a single plate-like member or a composite plate-like member by etching. Accordingly, the uniform holes or indentations can be formed in the thickness direction so that the irregularities of the gap between the cathode wires (electron emitting sources) and the control electrodes can be reduced.
(18) In a display device comprising a rear panel having a plurality of cathode wires having electron emitting sources, a plurality of control electrodes which cross the cathode wires and control an emission quantity of electrons from the electron emitting sources in response to the potential difference between the cathode wires and the control electrodes and a rear substrate, and a face panel having anodes and fluorescent materials, the control electrodes are formed of plate-like members and include a plurality of holes per one of first regions thereof which cross the cathode wires, and in one of the first regions, no insulation layer is disposed between regions formed between the plurality of holes and the cathode wires, and the cathode wires have the electron emitting sources having an area smaller than an area of the holes corresponding to the holes.
Since the area of the electron emitting sources is smaller than the area of the holes of the control electrodes, it is possible to make electrons emitted from the electron emitting sources pass in the anode direction without any loss so that images of high brightness can be obtained with low electric power consumption.
(19) In a display device comprising a rear panel having a plurality of cathode wires having electron emitting sources, a plurality of control electrodes which cross the cathode wires and control an emission quantity of electrons from the electron emitting sources in response to the potential difference between the cathode wires and the control electrodes and a rear substrate, and a face panel having anodes and fluorescent materials, the control electrodes are formed of plate-like members, the control electrodes include holes in regions thereof which cross the cathode wires, the control electrodes include projecting portions between the neighboring cathode wires, and the control electrodes are supported by the projecting portions. Accordingly, the control electrodes can be supported in a more stable manner.
Here, it is needless to say that the present invention is not limited to the above-mentioned constitutions and constitutions of embodiments which will be explained later and various modifications are conceivable without departing from the technical concept of the present invention.